1. Field of the Invention
The present invention relates to non-contacting measuring systems for acquiring the position of two coordinate systems with sensors, particularly of a stationary coordinate system lying in a measuring plane and of movable coordinate system, particularly for acquiring the absolute precision and repetitive accuracy of industrial robots. The acquisition of the position of two coordinate systems arises not only when concerned with industrial robots (IR) but arises quite generally in automatic processing procedures, for example with machine tools relative to the work pieces to be processed.
2. Description of the Prior Art
Industrial robots offer a repetitive or reproducing accuracy that lies at a few 1/10 mm up to 2-3/100 mm, dependent on the size and working area of the industrial robot. The repetitive accuracy is the capability of the industrial robot to repeatedly approach a tool reference point in the working area with prescribed position and orientation with the indicated precision, whereby identical boundary conditions prevail, for example identical movement path, identical load, speed, type of movement, etc.
In addition to the foregoing, the utilization of the industrial robot for the programming of the positions and movements (teach-in programming) is critical for the formulation of the repetitive accuracy for positioning a tool/workpiece with industrial robots.
When the positions are generated in a purely numerical fashion by sensors (for example, image evaluation systems) or by computer assisted design (CAD) assisted off-line programming systems or, respectively, programs are also merely transferred from other, similarly constructed robot systems, then the absolute precision of the industrial robot is decisive. The absolute accuracy of an industrial robot is therefore the capability of approaching a numerically defined spatial point (position x, y, z plus orientation) with indicated precision with respect to a defined coordinate system. The corresponding dependency of this characteristic on various parameters such as, for example, position or attitude in the working area, motion path, load, etc, must be identified and statistically interpreted for a qualified investigation of industrial robot precision characteristics (Robotics and Computer Integrated Manufacturing, Vol. 2, No. 3/4, 1985, pp. 261-278 and 247-259).
The measurement of the repetitive accuracy of industrial robots was usually undertaken heretofore by measuring sensors or high-accuracy proximity sensors that are arranged in three planes residing perpendicularly to one another, and by a corresponding measuring cube that was secured to the robot hand (European Patent No. 0 136 413). Since the robot with the measuring cube can enter into the measuring corner only from one direction, and expansion, for example approaching the measuring position from different directions, is difficult.
Various measuring methods are known for measuring the absolute precision; these, however, are either extremely involved and expensive or, respectively, are too inaccurate or timeintensive (The Industrial Robot, March 1986, pp. 53-54).